Abarim Publications' online Biblical Hebrew Dictionary
The demonstrative pronoun and adverb זה (zeh) or זו (zo) or זאת (zo't; feminine), meaning that or which, happens in various but comparable forms all over the Semitic language area. It probably has nothing to do with the root זהה (zhh). Although it looks related, the similarity is coincidental; our particle is an expanded form of what in antiquity was probably just the letter ז (zayin).
Often our particle is used as a substantive, for instance in Genesis 2:23: 'This one (זאת) is bone from my bone; this one shall be called woman.' Sometimes it's repeated: 'Thus this one did not come near that one all night' (Exodus 14:20). But mostly it points reflectively to whatever comes next, or whatever it follows: 'This bread of ours...' (Joshua 9:12), 'this great nation...' (Deuteronomy 4:6), 'Look at this...' (Job 5:27).
In combination with other particles it forms clever but sometimes hard to interpret formulas: אי־זה would mean 'where, then...?' (Job 28:12); בן־מי־זה literally means 'the son - of whom - this is...?' (1 Samuel 17:55); and the famous מי זה מלך הכבוד, means 'Who is this king of glory...?' (Psalm 24:8).
Slightly more challenging is the use of our particle on poetic slants: הר־ציון זה שכנת בו, 'Mount Zion this you dwelt in it' (Psalm 74:2). It occurs with particles such as ב (be) meaning 'in', forming בזה meaning 'in this' (Genesis 38:21) or 'then' (Esther 2:13), or בזאת, meaning with this, or under these conditions (Genesis 34:15). With כ we get כזאת meaning the like of this, or as follows (Genesis 45:23), or things such as these (Judges 13:23). With מ we get מזה meaning 'from here' (Genesis 37:17).
In a little more than a dozen times our particle is spelled as זו (zo), which happens to be identical to the name Ziv, the month of the blossoms: Exodus 15:13, Psalm 68:28, Hosea 7:16, Habakkuk 1:11. Our combo-particle בזה is spelled identical to a cluster of words that have to do with the verbs בזה (baza), meaning to disdain, and בזז (bazaz), meaning to plunder.